1. Field of the Invention
The present invention relates to a lamp, and more particularly, to a fluorescent lamp that can be easily manufactured to provide high brightness and high efficiency, a method of manufacturing the same, and a backlight unit having the same.
2. Description of the Related Art
Flat panel display devices include plasma display panels, field emission displays, light emitting diodes, and liquid crystal display devices (LCD).
In an LCD, data signals are supplied to pixels arranged in an active matrix configuration and light transmittance is adjusted by the displacement of liquid crystal according to the supplied data signals to display an image.
However, the LCD is not self-luminous and thus must receive light from an external light source.
Accordingly, a backlight unit serving as the external light source is provided on the bottom surface of the LCD. The backlight unit is categorized into an edge type backlight unit and a direct type backlight unit according to the arrangement of lamps.
The edge type backlight unit includes a lamp disposed on the side surface thereof to emit light to a side direction, a light guide plate converting the emitted light into surface light and guide the surface light in a forward direction, a reflection plate disposed on the bottom surface of the light guide plate to reflect the light in the forward direction, and an optical sheet diffusing the light from the light guide plate and adjusting the propagating direction of the light.
The direct type backlight unit includes a plurality of lamps disposed on a plane spaced apart from one another by a predetermined distance to emit light, a reflection plate disposed on the bottom surfaces of the lamps to reflect the emitted light in a forward direction, and an optical sheet diffusing the light from the lamps and adjusting the propagating direction of the light.
The lamp of the edge type and direct type backlight units may be a cold cathode fluorescent lamp (CCFL) or an external electrode fluorescent lamp (EEFL).
The CCFL can emit high-brightness light, but it is complex and expensive to manufacture.
Therefore, researches are actively conducted on the EEFL in recent days.
FIGS. 1A and 1B are sectional views of related art EEFLs.
Referring to FIG. 1A, a related art EEFL includes a glass tube 1 and first and second electrodes 3 and 4 that are formed respectively at both end portions of the glass tube 1. An inner surface of the glass tube 1 is coated with a phosphor 2 and an inner space thereof is filled with gas. The first and second electrodes 3 and 4 are formed to cover the both end portions of the glass tube 1.
When a voltage is applied across the first and second electrodes 3 and 4, electric charge is generated on inner surfaces of the both end portions of the glass tube 1. Due to the generated electric charge, the gas in the glass tube 1 is ionized by discharge. The ionized gas reacts on the phosphor 2 to generate light.
As described above, electric charges are generated in both inner end regions of the glass tube 1 that correspond to both outer end surfaces contacting the first and second electrodes 3 and 4.
However, the end region of the glass tube 1 has the same diameter as the center region thereof, and the area of the outer end region contacting the electrode is determined according to the length of the electrode. Therefore, the region where the electric charges are generated cannot be extended. Accordingly, it is difficult enhance the brightness and efficiency of the EEFL.
Referring to FIG. 1B, another related art EEFL includes a glass tube 5 and first and second electrodes 7 and 8 that are formed respectively at both end portions of the glass tube 5. An inner surface of the glass tube 5 is coated with a phosphor 6 and an inner space thereof is filled with gas.
Unlike the glass tube 1, the glass tube 5 has the end portion that is formed in a balloon so that the contact area between it and the electrode can be extended to generate greater electric charge in the inner surface of the glass tube 5. Accordingly, the EEFL of FIG. 1B has higher brightness and efficiency than the EEFL of FIG. 1A.
However, it is difficult, complex and time-consuming to form the end portion of the glass tube in a balloon shape. Also, it is difficult to form the balloon-shaped end portions of the glass tubes uniformly for every EEFLs.